Experimental and Theoretical Studies of Ultrafine Pd-Based Biochar Catalyst for Dehydrogenation of Formic Acid and Application of In Situ Hydrogenation

Abstract

In this work, a novel “foaming” strategy uses sodium bicarbonate (NaHCO3) and ammonium oxalate ((NH4)2C2O4) as the foaming agent, turning biomass-derived carboxymethyl cellulose (CMC) into N-doped porous carbon. Highly active palladium nanoparticles (Pd NPs) immobilized on nitrogen-doped porous carbon (Pd@MC(2)-P) are produced through a phosphate-mediation approach. The phosphoric acid (H3PO4) becomes the key to the synthesis of highly dispersed ultrafine Pd NPs on active Pd-cluster-edge (the edge of the Pd-cluster-100 and Pd-cluster-111 surfaces). The Pd@MC(2)-P exhibits high activity for formic acid (FA) dehydrogenation with an initial TOFg of 971 h–1 at room temperature. The subsequent hydrogenation of phenol using FA as an in situ hydrogen source on Pd@MC(2)-P and the highly efficient hydrogenation of phenol to cyclohexanone reaches more than 90% selectivity and 80% conversion. Density functional theory (DFT) calculations reveal that the reduced H poisoning and more exposed (100) surface over Pd nanoparticles are the keys to the Pd nanoparticles’ high activity.

Efficient Dehydrogenation of Formic Acid at Room Temperature Using a Pd/Chitosan-Derived Nitrogen-Doped Carbon Catalyst: Synthesis, Characterization, and Kinetic Study

“…By substituting the four rate constants into the Arrhenius equation (Figure c), the activation energy of the Pd 9.2 /C–N catalyst can be calculated as 39.15 kJ mol –1 . In this way, the activation energy ( E a ) of Pd 9.2 /C–N catalyst is lower than that of the reported values of formic acid dehydrogenation reaction. ,,, The corresponding TOF values were 766, 997, 1297, and 2593 h –1 . The TOF values are relatively high in the dehydrogenation reaction of formic acid at low concentrations (0.37 M).…”

“…In this way, the activation energy (E a ) of Pd 9.2 /C−N catalyst is lower than that of the reported values of formic acid dehydrogenation reaction. 18,27,29,36 The corresponding TOF values were 766, 997, 1297, and 2593 h −1 . The TOF values are relatively high in the dehydrogenation reaction of formic acid at low concentrations (0.37 M).…”

“…This suggests a strong interaction between support and metal with electron transfer from graphitic-N and pyridinic-N to Pd. The strong interaction effect protects the zerovalent palladium on the Pd 9.2 /C−N surface from being oxidized 18 and simultaneously enhanced its catalytic performance.…”

“…Therefore, widely sourced, low-cost, and environmentally friendly biochar materials have become the research focus. 17,18 One-step preparation of N-doped biochar support materials can be achieved by using nitrogen-rich (∼7 wt % 19 ) renewable bioresource chitosan as the precursor. 20,21 Chitosan is environmentally friendly with low toxicity, excellent biocompatibility, and biodegradability.…”

Hydrogen Production via Cerium-Promoted Dehydrogenation of Formic Acid Catalyzed by Carbon-Supported Palladium Nanoparticles

“…As palladium (Pd) is the most active metal for aqueous formic acid dehydrogenation, Pd-based catalysts have been extensively used. Pd alloyed with Ag, Au, Cu, Co, or Ni showed considerably improved activity compared to monometallic Pd catalysts. ,− Adopting novel supports or modifying supports with dopants such as nitrogen, amine-functional groups, and metal oxide also was used in a way to enhance the activity of Pd-based catalysts. − ,− These enhanced catalytic activities were attributed to the particle size of active metals, ligand effect (electronic modification), strain effect (changes in lattice distance), and interaction of dopants with reactants or intermediates, and in most cases, a combination of these effects. Despite the considerable improvement in catalytic activity, ironically, such combined effects make it difficult to understand the independent role of each factor in the formic acid dehydrogenation reaction.…”